Resistor



Sept. 17, 1940. N. E. LINDENBLAD RESISTOR Filed Nov. 12, 1935 s Sheets-Sheet 1 INVENTOR NILS E. LINDENBLAD wg A TORNEY P 1940- N. E. LINDENBLAD RESISTOR Filed Nov. 12, 1956 5 Sheets-Sheet 2 INVENTOR NILs Ll DENBLAD BY ATTORNEY Sept. 17, 1940. N. E. LINDENEJLAD RESISTOR Filed Nov. 12, 19156 5 Sheets-5heet -5 INVENTOR NILS LINDENBLAD ATTORNEY Patented Sept. 17, 1940 UNITED STATES RESISTOR Nils E. Lindenblad, Rocky Point, N. Y., asaignor to Radio commtion of America, a corporation of Delaware Application November 12, 1936, ScriaiNo. 110,415

3 Claims. (Cl. 201-63) This invention relates to new and novel resistors of small internal and stray capacitance which are particularly adapted to high frequency circuits.

5 An object of this invention is to simplify and improve small capacity resistors generally.

Another object of this invention is to increase the loading capability in general of resistors of low internal and stray capacitance, in other words, to provide a resistor of low internal and stray capacitance with improved means of heat dispensation.

It can also be stated that by this invention, there is provided resistor units of small physical .5 dimensions having low values of distributed capacitance and capacitance leakage to the surrounding supporting elements. I

Thus, one of the objects of this invention is to provide a small resistor with increased cooling means so that it will be able to carry a higher current load. The gain from this procedure is then that the resistor can be made very small and thushave low internal as ,well as stray capacitance, which is an important feature in ;5 short wave or high frequency circuits, such as in resistance coupled amplifiers handling wide frequency bands. An increased capacitance effect will cause an increasing reactive (capacitively reactive) current to be introduced at the higher frequencies together with the current determined by the resistive values which will result in undesired distortion.

A feature of this invention is the placing of a resistive material in an efficient electrical in- 5 sulating and cooling medium to reduce the physical dimensions of the resistor.

Another feature of this invention is the method of making improved enclosed resistor units and also the means of supporting and connecting 0 them in a circulating fluid cooling system. The improved resistor of this invention may be used in the circuit of a high power, resistance coupled linear amplifier for very high frequencies in the order of 20,000,000 to 2,000,000 cycles. The in- 5 herent capacitance of the ordinary resistor becomes a serious factor that must be reckoned with when used in high frequency circuits. The outstanding factors contributing to-the undesired capacitance effects of resistors known 0 in the prior art are the large physical dimension of the ordinary resistors made necessary because of the need for heat dissipation, the spacing oi. the wires, the dielectric constant of the binder for the wires, and the method of the distribu- 5 tion of the binder, also the d electric constant of the mechanical support for the wires or resistanee material.

There have been several methods suggested in the past to reduce the above mentioned factors to a fair minimum as, for example, by the use 5 of materials having high heat resistivity and also by supporting the wires or resistive element by a minimum amount of insulating material and allowing air currents to freely circulate around the resistance wire; however, such methods are still unsatisfactory for the higher frequencies.

Briefly, by my invention I propose to greatly improve the low capacitance resistors known in the prior art by mounting the resistance element within a tube of very high grade insulating materialwhich at the high frequencies has a minimum dielectric effect upon the capacitance. The resistance element may be either that of a coated film, a wire, or a filament; the resistivity of the material may be of a high or low value. The tube of insulating material has a physical length greater than the length of the resistance element. The resistance element is placed within a circulating fluid system. By the term minimum dielectric effect I mean the use of a good dielectric material, that is, a material having a low dielectric loss, to mechanically support the resistive element so that the dielectric constant of the resistor portion of a high frequency circuit will be small and the losses low when the resistor is placed in high frequency circuits. Although a resistive element which is a conductor has only pure resistance when placed in a direct current circuit, when placed in a high frequency circuit, the resistor 'portion of the high frequency circuit has in addition to the resistance, a series inductance which is caused by the length of the conductor and also its shape. Likewise, in shunt with the resistance 40 and the series inductance, there is a shunt capacitance, this capacitance being caused by the insertion of some form of mechanical support which in this invention is the glass tube 2, and therefore as it is desirable to'keep the dielectric losses to a minimum, it becomes necessary to employ as little insulating material in the circuit as possible. Likewise, it is desirable to keep the dielectric constant of the material low so. that the total dielectric effect is maintained at a minimum amount.

This invention will best be understood by referring to the accompanying drawings, in which:

Fig. 1 is a schematic diagram of a fluid circulating coil system;

Fig. 2 is a detailed view of the improved resistor element located within a tube of material having a minimum low dielectric constant at the high frequencies;

Fig. 3 is a plan view of Fig. 2;

Fig. 4 is a modification of Figs. 2 and 3 wherein the resistance element is a straight resistance wire;

Fig. 5 is a modification of Figs. 2, 3 and 4 wherein the resistance element is in the form of a helical coil of resistance wires; while Fig. 6 is a schematic diagram showing a modification of Fig. 1;

Fig. 7 is a schematic diagram of a water cooling system; and

Fig. 8 is a schematic diagram of an air cooling system.

Referring now in detail to Fig. 1, a schematic diagram is shown of a symmetrical arrangement of two resistors located within a circulating fluid and electrical insulating system such as oil, or the like. The resistance element l is shown located within the tubes 2 which are of high grade insulating material having a minimum dielectric effect, such as Pyrex, glass, isolantite, etc. The insulating tubes 2 are secured to a mounting panel 3 by means of fianges 4 and are coupled to circulating metallic pipes 5 and 6 by means of coupling fittings I and 8. The upper pipe 5 is connected to the top of a fluid radiator 8 of copper, which is provided with cooling fins III. This radiator can be additionally cooled by an external water circulating or refrigeration system, air blast, etc. The lower circulating pipe 6 is coupled to the radiator at a point The other half of the symmetrically arranged cooling system is arranged similarly to that mentioned above, except that there is provided a tube l2 which is of necessity longer than section 5 due to the fact that it is located at a greater distance from the radiator 9. Likewise, at the lower portion of the radiator, a circulating tube M is connected to the lower portion of the resistance tube 2.

In Figs. 2 and 3, there is shown in detail the preferred embodiment of this invention wherein resistance element 1 is in the form of a metallized coating on the central portion of the inner wall of insulating tube 2. The ends of the coating IA terminate in a metal-like band 20 which is connected to a hollow terminal stud 2| through which a wire 22 connects band 20 with terminals 2| To protect the supporting and sealing tip 23, there is provided a metallic bell-like member 24. The terminal 2| is provided with suitable nuts 25 and washers 26. To provide fluid type connections to the insulating tube 2, there is provided in each end of the tube a series of grooves l9 to which any suitable coupling fitting is fastened such as rubber hose with metallic bands surrounding the grooved portion IS. A coated resistor is particularly valuable in circuits where also a low inductive reactance is desirable. The coating of the resistor may, of course, be on either or both sides of a strip or on the inside, outside or both of a cylinder. The cylinder may also be the resistance material, itself. The main feature is that they should be immersed in an efllcient cooling insulating medium so that the physical dimensions of the resistor may be reduced. Further information relative to the resistance film formed on an insulating surface may be had by referring to the Hansel] docket 11088, filed Feb. 6, 1936, Serial No. 62,587.

The modification shown in 4 is of similar construction to that of Figs. 2 and 3, except that instead of the coated film within the inner wall of the tube 2, the resistive element is in the form of a non-inductive metallic rod-like resistance 21. This rod may be of any suitable resistance material such as Monel metal, nickel silver, Nichrome, Advance, or the like. The resistance rod 2'I is located substantially in the central portion of tube 2 and may be of any suitable configuration such as a ribbon square or round rod of that of a wave band with a wave-like configuration to provide increased cooling surface yet suiticiently limited in curvature to prevent the formation of undesired electrical inductance.

The tube 2 is provided with terminal members similar to that mentioned above with reference to Figs. 2 and 3 and the ends of the tube are provided with grooves l9 to provide fluid type connections with suitable coupling means.

Referring now to Fig. 5, a resistance wire 30 in the form of a helical coil is located substantially in the center of the insulating tube 2. Each end of the coil is provided with a hollow terminal stud l5 through which wire I is soldered at a point l6, electrical connections being taken from stud I5 and secured by means of nuts l1 and washers l8, Fluid-tight connections are made to the insulating tube as described above, with reference to Figs. 2 and 3, by providing in each end of the tube a series of grooves I9 to which any suitable coupling fitting is fastened. This helical form naturally has a large amount of electrical inductance; therefore, its use is more limited when placed in a high frequency circuit than the form shown by Figures 2, 3 and 4.

The schematic diagram shown by Fig. 6 is generally similar to that of Fig. 1, except that the lower pipes S and H of the circulating fluid system are provided with a pump to force the fluid in circulation, whereas the system shown in Fig. 1 is that generally known as the thermosyphon system. The circulating fluid for either system can be either hydrogen, oil or any other fluid having the requisite insulating qualities.

The radiator 9 may also be more or less integral with the panel of the set. The radiator may also be cooled by an external water circulating system, as shown by Fig. 7, wherein a tank 2|! contains a circulating fluid, such as water 2| or the like which may be circulated by a pump 22. Radiator 9 is supported in the bottom of the tank by supports 23; to provide a fluid-tight container bushings 2! are provided.

Fig. 8 shows a fan or blower 26 for blowing a blast of cool air upon radiator 9 and while only one fan or blower is shown, a greater number may be provided and arranged to cool any part of radiator 9, or fan 28 may be placed outside of tank 2| of Fig. 'i to provide additional cooling of the circulating fluid 2|.

This invention is not to be limited to the modifications shown as it is evident to those skilled in the art that the invention may take other forms within the spirit and scope of the same, and therefore should not be limited except by such limitations as are imposed in the appended claims.

What is claimed is:

1. In a. non-inductive resistance element for use in a high frequency circuit, an insulating tube open at each end and having substantially low dielectric effects upon said resistance when placed in said high frequency circuit, a metallic resistive element within said insulating tube, liquid cooling means for passing a liquid through said insulating and mechanical coupling means located at the ends of the tube for: coupling said resistance with said liquid cooling means.

2. In a non-inductive resistance element for use in a high frequency circuit, an insulating tube open at each end and having substantially low dielectric effects upon said resistance when placed in said high frequency circuit, a metallic resistive element within said insulating tube.

liquid cooling means for passing oil through said insulating, tube to cool said resistive element, terminal means including a projecting'portion provided within the side walls of said tube for connecting the resistance with a hollow stud for providing external connections to said high frequency circuit, and mechanical coupling means located at the ends of the tube for coupling said resistance with said liquid cooling means.

3. In a non-inductive resistance element for use in a high frequency circuit, an insulating tube open at each end and having substantially low dielectric effects upon said resistance when placed in said high frequency circuit, a metallic resistive element within said insulating tube, liquidcooling means for passing a liquid through said insulating tube to cool said resistive element, terminal means including a projecting portion provided Within the side wallsof said tube. a metal band connected to said terminal means for connecting the resistance with a hollow stud for providing external connections to said high frequency circuit, and mechanical coupling means located at the ends oi. thetube for coupling said resistance with said liquid cooling means. 7 

